Timepiece designers have always endeavoured to increase the reliability of movements, as a result of reducing the frequency of maintenance operations, while ensuring accurate operation of the timepiece movements.
The lubrication of wheels and pinions and moving components is a difficult problem to resolve. Lengthy tribological testing is required to develop solutions to simplify or even eliminate lubrication.
More specifically, it is sought to achieve lubrication-free operation of escapement mechanisms, by attempting to define pairs of materials in friction contact having a low and stable coefficient of friction and low wear, and exhibiting excellent resistance over time.
EP Patent Application No 0732635A1 in the name of CSEM discloses the manufacture of a micromechanical component, particularly a pallet lever of an escapement, with a friction surface including silicon nitride, in an unspecified composition. This document envisages a pair with a counter-piece, with improved tribology: this document cites a titanium nitride against titanium carbide pair, or a titanium nitride against silicon carbide pair.
The document XP XP002734688, “A study of static friction between silicon and silicon compounds”, by Messrs Deng and Ko, describes the use in precision micromechanics of the silicon nitride-silicon pair, for low wear over time, and improved tribology.
The document XP002734924, “LPCVD against PECVD for micromechanical applications” by Messrs Stoffel, Kovacs, Kronsat, Müller discloses the use of non-stoichiometric silicon nitride, obtained by PECVD or LPCVD, to ensure tribological properties.